Always show copy button on touch devices

Button was invisible on mobile and tablet. Adds @media (hover: none)
rule so it shows where hover isn't available as a primary input.

Author: mattsafaii

main.css

@@ -319,7 +319,7 @@ pre > code:focus {
 } */
 
 /* Code */
-/* .highlight .hll { background-color: #ffc; 
+/* .highlight .hll { background-color: #ffc;
 .highlight .c { color: #999; }
 .highlight .err { color: #a00; background-color: #faa }
 .highlight .k { color: #069; }
@@ -731,3 +731,9 @@ pre:hover .copy-btn,
 .copy-btn:hover {
   background: rgba(171, 178, 191, 0.1);
 }
+
+@media (hover: none) {
+  .copy-btn {
+    opacity: 1;
+  }
+}